I've had the opportunity to see one of the infamous German drug tests in practice (wasn't driving). The result is that if you used any canabis 4 days earlier it will show up on the pee test. It was waved off as no issue, but four young Dutch people in car got their attention a bit too much apparently. If they thought we were the type they were looking for they had cause to do whatever. We were not the ones they were after though as we were not going to the nearby festival and were just driving by.